Hi Ze at distribution board, how would you approach?

[Gringoking88]

Hi all,

Looking to exploit (please) those older and wiser lol. I was asked to extend / relocate a cooker circuit (6mm t&e) and did so no problems. I then started doing the minor works, R1+R2 came in at 0.05 ohms so was perfect. However, I then went to do do an Ze at the board and get very high readings e.g. around the 6 ohms Mark, this obviously resulted in my Zs being outside acceptable values.

The first learn I guess is always do a Zs / Ze before you take a job (I know, a rookie mistake)! But the question is how would you guys approach this now e.g. what would you do with the minor works, would you advise the customer to contact dno then retest or just calculate Zs from the given Ze and complete the minor works when the Ze is rectified, or would you do a minor works now, note the customer needs to rectify Ze then reissue another minor works?

Many thanks in advance,

Martin.

 

[Ian1981]

You’d only need a 100mA rcd/rcbo to deal with the fault protection issue on a high zs tho depending if it’s protecting socket outlets or cables buried in walls or additional protection is needed for other reasons, then 30mA will be required.
As said a new circuit on a TN system should be designed that the mcb provides satisfactory fault protection for said circuit.

 

[Gringoking88]

Thanks all for the reply's!!! I also spoke to NICEIC technical helpline and they advised to exactly as Wilko said, A+ Wilko lol! I have advised customer to call DNO and given them the details of the fault etc. Said I would retest when its rectified at no cost. They seemed very happy that I actually cared and didnt just make up the certificate lol

 

[Wilko]

Oh dear, I must've put the radio on NIC FM

 

[Gringoking88]

Oh dear, I must've put the radio on NIC FM

LOL, What I am confused about, or perhaps, I should say, there is confusion about is; if the Ze is high, some have suggested the circuit should not be energised, but this fault would affect the entire property so would you therefor not turn off the entire installation??? Not sure how the property owner would feel about that lol.

 

[Toneyz]

Oh dear, I must've put the radio on NIC FM

Replacement of Tony Cable job vacancy filled.

 

[Wilko]

Yes the fault affects the whole property, but you've modified one circuit. My view is the circuit is "out of normal service" during your work (including the live tests) and by testing you know it does not meet the intended design. So the circuit should not be returned to "normal service" by you.

 

[westward10]

LOL, What I am confused about, or perhaps, I should say, there is confusion about is; if the Ze is high, some have suggested the circuit should not be energised, but this fault would affect the entire property so would you therefor not turn off the entire installation??? Not sure how the property owner would feel about that lol.

Yes judge I was fully aware of the possible outcome of making the circuit live knowing the earth was not satisfactory.

 

[lurch]

Agree with all those that state advise dno to rectify but hypothetically or technically what is the difference of a tt System with zs readings sub 200 ohms?
Edit to say c/w 30ma rcd

 

[Wilko]

To me the difference is - if it was TT it would be working as per its design - if it's a TN then it has a fault, which could get worse ...